全文获取类型
收费全文 | 16155篇 |
免费 | 1011篇 |
国内免费 | 804篇 |
专业分类
电工技术 | 751篇 |
技术理论 | 1篇 |
综合类 | 1919篇 |
化学工业 | 1707篇 |
金属工艺 | 466篇 |
机械仪表 | 888篇 |
建筑科学 | 2317篇 |
矿业工程 | 564篇 |
能源动力 | 754篇 |
轻工业 | 878篇 |
水利工程 | 860篇 |
石油天然气 | 1093篇 |
武器工业 | 156篇 |
无线电 | 556篇 |
一般工业技术 | 1372篇 |
冶金工业 | 891篇 |
原子能技术 | 139篇 |
自动化技术 | 2658篇 |
出版年
2024年 | 42篇 |
2023年 | 130篇 |
2022年 | 291篇 |
2021年 | 366篇 |
2020年 | 370篇 |
2019年 | 313篇 |
2018年 | 303篇 |
2017年 | 334篇 |
2016年 | 435篇 |
2015年 | 494篇 |
2014年 | 1024篇 |
2013年 | 920篇 |
2012年 | 1041篇 |
2011年 | 1306篇 |
2010年 | 990篇 |
2009年 | 1007篇 |
2008年 | 982篇 |
2007年 | 1128篇 |
2006年 | 1093篇 |
2005年 | 952篇 |
2004年 | 873篇 |
2003年 | 762篇 |
2002年 | 603篇 |
2001年 | 468篇 |
2000年 | 346篇 |
1999年 | 292篇 |
1998年 | 205篇 |
1997年 | 173篇 |
1996年 | 151篇 |
1995年 | 118篇 |
1994年 | 88篇 |
1993年 | 89篇 |
1992年 | 59篇 |
1991年 | 48篇 |
1990年 | 33篇 |
1989年 | 18篇 |
1988年 | 12篇 |
1987年 | 12篇 |
1986年 | 8篇 |
1985年 | 9篇 |
1984年 | 10篇 |
1983年 | 8篇 |
1981年 | 4篇 |
1980年 | 6篇 |
1979年 | 6篇 |
1974年 | 3篇 |
1965年 | 3篇 |
1957年 | 5篇 |
1956年 | 5篇 |
1955年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
María Fernndez Alicia de Coo Ins Quintela Eliane García Mrcio Diniz-Freitas Jacobo Limeres Pedro Diz Juan Blanco ngel Carracedo Raquel Cruz 《International journal of molecular sciences》2021,22(12)
Severe periodontitis is prevalent in Down syndrome (DS). This study aimed to identify genetic variations associated with periodontitis in individuals with DS. The study group was distributed into DS patients with periodontitis (n = 50) and DS patients with healthy periodontium (n = 36). All samples were genotyped with the “Axiom Spanish Biobank” array, which contains 757,836 markers. An association analysis at the individual marker level using logistic regression, as well as at the gene level applying the sequence kernel association test (SKAT) was performed. The most significant genes were included in a pathway analysis using the free DAVID software. C12orf74 (rs4315121, p = 9.85 × 10−5, OR = 8.84), LOC101930064 (rs4814890, p = 9.61 × 10−5, OR = 0.13), KBTBD12 (rs1549874, p = 8.27 × 10−5, OR = 0.08), PIWIL1 (rs11060842, p = 7.82 × 10−5, OR = 9.05) and C16orf82 (rs62030877, p = 8.92 × 10−5, OR = 0.14) showed a higher probability in the individual analysis. The analysis at the gene level highlighted PIWIL, MIR9-2, LHCGR, TPR and BCR. At the signaling pathway level, PI3K-Akt, long-term depression and FoxO achieved nominal significance (p = 1.3 × 10−2, p = 5.1 × 10−3, p = 1.2 × 10−2, respectively). In summary, various metabolic pathways are involved in the pathogenesis of periodontitis in DS, including PI3K-Akt, which regulates cell proliferation and inflammatory response. 相似文献
132.
针对某离散制造企业的业务流程,采用C/S(Client/Server)结构模式,使用VB6.0作为前台开发工具,SQL Server2000做后台数据库,开发了企业进销存管理系统。该系统以企业管理的计划和控制职能为核心,提供了采购、库管、销售、计划等实用而丰富的管理功能,可以对企业的经营管理活动分析、预测。文章介绍了系统的建模、设计和实现过程。 相似文献
133.
134.
船舶钢板激光弯曲成形的实验研究 总被引:6,自引:0,他引:6
在对船舶钢板激光弯曲成形过程进行实验研究中,采用CO2激光器研究了激光功率、扫描速度、扫描次数以及钢板厚度对船舶钢板激光弯曲成形的影响规律。实验中实时测量了船舶钢板激光弯曲成形过程钢板弯曲角度和温度的变化。结果表明:钢板弯曲角度随激光功率的增加而增加,随激光束扫描速度的增加而减小,而且随着钢板厚度的增加,弯曲角度减小;激光工艺参数和钢板厚度都对钢板激光多次扫描成形产生影响,钢板的弯曲角度随着激光扫描次数的增加而增加。对于较薄的船舶钢板,钢板弯曲角度随扫描次数增加近似呈线性增加,而较厚的钢板,随扫描次数的增加,钢板弯曲角度的增加逐渐减小。 相似文献
135.
136.
137.
W. Dennis Pocklington 《Journal of the American Oil Chemists' Society》1992,69(8):789-793
The development, by collaborative study, of a standardized method for the determination of tetrachloroethylene in olive oils
is described. The results of the study, which was carried out in 1989 under the direction of the International Olive Oil Council
(IOOC), are presented and show that tetrachloroethylene can be readily determined, to an acceptable degree of precision, by
gas-liquid chromatography with electron capture detection. A limited number of results obtained for the determination of trichloroethylene
and chloroform by the same method indicate that a similar precision could be obtained with the method when determining these
solvents also. 相似文献
138.
139.
Unni Olsbye Anastasia Virnovskaia Øystein Prytz Stan J. Tinnemans Bert M. Weckhuysen 《Catalysis Letters》2005,103(1-2):143-148
A Cr/Al2O3 alkane dehydrogenation catalyst exhibits a maximum in ethylene yield during an ethane dehydrogenation cycle. Isotopic labelling experiments with monolabelled 13C-ethane and deuterium were used to elucidate whether the initial activity increase could be due to formation of an active, larger hydrocarbon intermediate on the surface. The results strongly indicate that this is not the case, and instead point to a traditional reaction cycle involving adsorption of ethane to form an ethyl species, followed by desorption of ethene and hydrogen. Transient kinetic data suggest that ethane adsorption is the rate-determining step of reaction. 相似文献
140.
《Information and Software Technology》2014,56(1):40-53
ContextThe dependencies between individual requirements have an important influence on software engineering activities e.g., project planning, architecture design, and change impact analysis. Although dozens of requirement dependency types were suggested in the literature from different points of interest, there still lacks an evaluation of the applicability of these dependency types in requirements engineering.ObjectiveUnderstanding the effect of these requirement dependencies to software engineering activities is useful but not trivial. In this study, we aimed to first investigate whether the existing dependency types are useful in practise, in particular for change propagation analysis, and then suggest improvements for dependency classification and definition.MethodWe conducted a case study that evaluated the usefulness and applicability of two well-known generic dependency models covering 25 dependency types. The case study was conducted in a real-world industry project with three participants who offered different perspectives.ResultsOur initial evaluation found that there exist a number of overlapping and/or ambiguous dependency types among the current models; five dependency types are particularly useful in change propagation analysis; and practitioners with different backgrounds possess various viewpoints on change propagation. To improve the state-of-the-art, a new dependency model is proposed to tackle the problems identified from the case study and the related literature. The new model classifies dependencies into intrinsic and additional dependencies on the top level, and suggests nine dependency types with precise definitions as its initial set.ConclusionsOur case study provides insights into requirement dependencies and their effects on change propagation analysis for both research and practise. The resulting new dependency model needs further evaluation and improvement. 相似文献